TAPHONOMY AND AFFINITY OF AN ENIGMATIC

SILURIAN VERTEBRATE, JAMOYTIUS KERWOODI

WHITE

by ROBERT S. SANSOM* , KIM FREEDMAN*� , SARAH E. GABBOTT* ,

RICHARD J. ALDRIDGE* and MARK A. PURNELL**Department of Geology, University of Leicester, University Road, Leicester LE1 7RH, UK; e-mails r.sansom@le.ac.uk, sg21@le.ac.uk, ra12@le.ac.uk,

mark.purnell@le.ac.uk

�6 Wescott Road, Wokingham, Berkshire RG40 2ES, UK; e-mail kim.freedman@btinternet.com

Typescript received 14 July 2009; accepted in revised form 23 April 2010

Abstract: The anatomy and affinities of Jamoytius kerwoodi

White have long been controversial, because its complex

taphonomy makes unequivocal interpretation impossible

with the methodology used in previous studies. Topological

analysis, model reconstruction and elemental analysis, fol-

lowed by anatomical interpretation, allow features to be

identified more rigorously and support the hypothesis that

Jamoytius is a jawless vertebrate. The preserved features of

Jamoytius include W-shaped phosphatic scales, 10 or more

pairs of branchial openings, optic capsules, a circular, subter-

minal mouth and a single terminal nasal opening. Interpreta-

tions of paired ‘appendages’ remain equivocal. Phylogenetic

analysis places Jamoytius and Euphanerops together (Jamoytii-

formes), as stem-gnathostomes rather than lamprey related

or sister taxon to Anaspida.

Key words: Jamoytius, Euphanerops, phylogeny, taphonomy,

Vertebrata, Gnathostomata, Silurian.

White (1946) first described Jamoytius kerwoodi on the

basis of two specimens from a Lower Silurian (Llando-

very) horizon of the Lesmahagow inlier of Lanarkshire,

Scotland, and considered it to be the most primitive

known vertebrate. Numerous subsequent authors have

disputed this conclusion or have disagreed with aspects of

White’s (1946) interpretation (Data S1). Evidence from

additional specimens collected at Lesmahagow localities

(see Ritchie 1968, 1985 for synopses of locality and stra-

tigraphy details) prompted Ritchie (1960, 1963, 1968,

1984) to redescribe Jamoytius as an ‘unspecialized anas-

pid’, possibly related to the extant jawless vertebrates. As

shown by Plate 1, most of Ritchie’s (1960, 1968) interpre-

tations of the anatomical features of Jamoytius differ from

those of White (1946).

Despite Ritchie’s treatment, Jamoytius continued to

generate debate. Various authors challenged Ritchie’s

work (e.g. Janvier 1981; Forey and Gardiner 1981) or sug-

gested affinities with a range of subsequently discovered

fossils (e.g. Janvier and Busch 1984; Briggs and Clarkson

1987). Cladistic analyses of the jawless vertebrates (e.g.

Janvier 1981, 1996a, b; Forey 1984, 1995; Forey and Jan-

vier 1993) have also failed to clarify the affinities of

Jamoytius; the lack of agreement regarding its anatomical

homologies has meant that different analyses have used

different character codings. In addition to coding, choice

of the in-group taxa included in the phylogenetic investi-

gation has affected the placement of Jamoytius (Donoghue

et al. 2000; Donoghue and Smith 2001; Gess et al. 2006).

The position of Jamoytius on cladograms has conse-

quently not stabilized, though Jamoytius usually appears

as a sister taxon to the lampreys, the anaspids, or Eupha-

nerops longaevus Woodward, 1900.

Janvier and Lund (1983 2, p. 412) wrote, ‘These various

interpretations cause one to wonder about the degree of

imagination involved in the study of Jamoytius and other

fossils preserved as tarry impressions.’ So why has it

proved so difficult to produce a definitive interpretation

of Jamoytius and to determine its affinities? The principal

problem is one that affects interpretation of many prob-

lematic fossils – disentangling the different aspects of the

process of anatomical reconstruction. The selection of an

appropriate anatomical comparator upon which to base

hypotheses of homology (comparisons being drawn either

directly to a specific extant organism or clade, or indi-

rectly through a fossil intermediate) can be especially

problematic (Donoghue and Purnell 2009); the choice of

interpretative model needs careful justification on the

basis of characters present, preferably unequivocally, in

the fossils. In the case of Jamoytius, almost all workers

have considered it as a jawless vertebrate without explicit

justification, and consequently, anatomical interpretations,

P A L A 1 0 1 9 B Dispatch: 15.10.10 Journal: PALA CE: Archana

Journal Name Manuscript No. Author Received: No. of pages: 17 PE: Raymond

[Palaeontology, 2010, pp. 1–17]

ª The Palaeontological Association doi: 10.1111/j.1475-4983.2010.01019.x 1

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homology statements and phylogenetic analyses are all at

risk of circularity. Jamoytius is generally preserved in two

dimensions, and investigations have often concentrated

on relating the shape of its features to the three-dimen-

sional anatomical parts of presumably related organisms.

Different workers have alternatively described the same

circular features in Jamoytius as mouth, eyes and nasal

structures (Pl. 1 and Data S1). These interpretations are

thus inherently equivocal. Anatomical and phylogenetic

claims, and counterclaims, will continue to be insecure

without further information about the topology, compo-

sition and taphonomic history of anatomical features,

combined with explicit articulation of the methodology

used to reach anatomical interpretations.

MATERIALS AND METHODS

Topological reconstruction and comparative anatomy. In

order to address the problems of circularity and equivo-

cal interpretations, a stepwise methodology separating

topological considerations from anatomical interpreta-

tion was applied as advocated by Donoghue and Purnell

(2009). First, the features of the fossils were identified

and described (i.e. number and shape of distinct body

parts, and the topological relationship between those

body parts). By comparing specimens preserved in dif-

ferent orientations, three-dimensional reconstruction was

possible (cf. Briggs and Williams 1981; Purnell and

Donoghue 1999). Throughout this process of interpreta-

tion and reconstruction, no assumptions were made

about the affinities of the organism or the homology of

its features.

Following topological description, an explicitly justified

interpretative model was selected upon which to base

anatomical hypotheses. Putative homologies were identi-

fied through the consideration of topological relationships

between body parts (Rieppel and Kearney 2002) and were

informed by evolutionary and potential taphonomic

transformational sequences (i.e. assessing whether the

appearance of a feature, or its absence, represents the ori-

ginal anatomical condition, or the results of post-mortem

processes of decay and preservation). The intrinsic

properties and composition of the body parts provided

additional constraints on interpretations.

Following translation of topological structures into

anatomical interpretations, taxonomic assessments and

phylogenetic analyses were employed to investigate the

placement of the organism in an evolutionary context.

Elemental analysis. Topological data were complemented

by determination of the chemistry and preservation of

particular features to provide evidence of original histol-

ogy and ⁄or composition (e.g. Butterfield 2002; Gabbott

et al. 2004). Elemental mapping of some features of Ja-

moytius was performed on a LEO 435 VP Scanning Elec-

tron Microscope with an Oxford Instruments ISIS 300

EDX spectrometer operating in variable pressure mode at

10 Pascals with an accelerating voltage of 10 kV and a

beam current of 500 picoamps for 1000 frames (approxi-

mately 14 h of run time). The specimens analysed in this

study have not been subjected to hydrofluoric acid treat-

ment (Ritchie 1963, 1968); smaller specimens were

selected because of SEM chamber size limits.

Phylogenetic analysis. Data matrices were constructed in

MacClade 4.06 (Maddison and Maddison 2003). Heuristic

searches were performed using PAUP 4.0 (Swofford 2002)

with 1000 random sequence addition replicates and TBR

(Tree bisection and reconnection) branch swapping.

Where appropriate, characters were reweighted according

to their rescaled consistency indices. To investigate the

alternative topologies that satisfy phylogenetic relation-

ships proposed on the basis of molecular data, heuristic

searches were conducted using backbone constraint trees

constructed in MacClade 4.06 (see below).

Institutional abbreviations and publicly held material. NHM, Nat-

ural History Museum, London, P11284 (holotype), P11285,

P47784-7; AMS, Australian Museum, Sydney, F64401, F102841-

6; NMS National Museum of Scotland, Edinburgh, 1959.1,

1966.3.1-3; BGS, British Geological Survey, Keyworth, 11882-3;

Hunterian Museum, Glasgow, V.7792, V.8036V.8141, V.8148,

GLHAM101382; UOE, University of Edinburgh, FR1628,

FR1476, 20129-32, 20145, 20159-62.

BODY PARTS, TOPOLOGICALANALYSIS AND RECONSTRUCTION

Body shape

In general aspect, Jamoytius has an elongate lozenge-

shaped body exhibiting a size range of 140–180 by 30–

EXPLANATION OF PLATE 1

Jamoytius kerwoodi White holotype (NHM P11284a) immersed in 90 per cent ethanol with incident polarized light and filter,

illustrating the conflicting interpretations of White (1946), in bold, and Ritchie (1960, 1963, 1968, 1984) in plain text. Scale bar

represents 10 mm.

2 PALAEONTOLOGY

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SANSOM et al., Jamoytius kerwoodi

eye

mouth

intermuscle spaces

(myocommata)

interscale spaces

displaced skin

lateral �n fold

basal supports

of anal �n

not interpreted

lateral �n fold

ventral termination

of body scales

notochord

one margin

of intestine

rays of

dorsal �n

not interpreted

bifurcation of

notochord

branchial basket

eye

eye

basal supports

of dorsal �n

not interpreted

intestine

one margin

of intestine

not interpreted

eye

lateral �n fold

branchial basket

muscle blocks

(with muscle �bres)

unmineralized scales

(with ornamentation)

COLOUR

PLATE 1

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40 mm. The body is preserved with a varying degree of

curvature (range of 40–90 degrees through the long axis

of the body). One end of the body of Jamoytius shows a

greater degree of morphological differentiation, contain-

ing multiple different substructures. This is provisionally

taken to be the head (see later discussion), thus indicating

anterior. Through comparison of paired and symmetrical

body parts, specimens are identified as collapsed remains

of a bilaterally symmetrical organism preserved in differ-

ent orientations (some are dorso-ventrally collapsed, some

laterally and others intermediate).

There is not enough evidence to determine the original

shape of the posterior of the organism, as most slabs do

not possess the most posterior portion. When present,

the posterior is preserved much more faintly than the rest

of the body, sometimes too faintly to be discerned clearly.

NHM P47784a exhibits what could be interpreted as two

posterior lobes, but the region is poorly preserved and

heavily prepared, thus obscuring the original body out-

line.

Body parts

Anterior subcircles. Four subcircles occur in the anterior

region. From comparison of specimens preserved in dif-

ferent orientations, it is apparent that they are coincident

with the body margin. Two distinct types of subcircle

occur. Two have broad, dark margins and form a lateral,

symmetrical pair, close to either the dorsal or ventral

body margin (Text-fig. 1). Comparison of the shapes of

these structures in dorso-ventral and laterally collapsed

specimens indicates that their original shape was either a

laterally flattened spheroid, or an outwardly opening cup-

like structure roughly equating to half or two-thirds of a

sphere (e.g. Text-fig. 1A). The other two subcircles have

narrower margins and lie along the sagittal plane, one ter-

minal, one subterminal in position (Text-fig. 1C,D). Irre-

spective of the orientations of the body, these axially

located rings are preserved as approximately circular out-

lines. This indicates either that they were originally spher-

ical, or that they were discs with sufficient rigidity at the

time of body collapse to reorient into a bedding parallel

attitude.

Elemental mapping analysis performed on the anterior

region of NHM P47787a shows a clear correlation of car-

bon with one of the paired, broader margined, anterior

subcircles (Text-fig. 2B).

Serial subrectangles. Towards the anterior end, many

specimens preserve a pair of linear features composed of

serially repeated, contiguous, subrectangular shapes

A B

C

A B C D

D

TEXT -F IG . 1 . 8Anterior subcircles of

Jamoytius (A–D) with corresponding

graphic interpretations (below), where

darker grey represents laterally paired

subcircles with broader margins, lighter

grey represents subterminal ring and

medium grey represents terminal ring.

A, NHM P11284a. B, NMS 1966.3.2. C,

NHM P11285. D, NMS 1966.3.1. Scale

bars represent 5 mm.

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(Text-fig. 3A,B). The central areas of the subrectangles

have the same coloration as the body but their perime-

ters are darker. Like the anterior subcircles, the lines of

subrectangles are coincident with the body margin. The

subrectangles are arranged in a ladder-like line, which

lies at a shallow angle to the antero-posterior axis of

the body.

The precise number of subrectangles is difficult to

establish and possibly varies between individuals. Jamoy-

tius has been reported to have had as many as 17 subrec-

tangles in each series (Ritchie 1984) and as few as seven

(Forey and Gardiner 1981). In the case of the specimen

discussed by the latter, the body is incomplete and the

posterior portion of the region with subrectangles may be

missing. On all specimens for which the entire length of

the line of subrectangle rows is present, at least 10 can be

identified, and on several, at least 14 (e.g. Text-fig. 3).

W-shaped structures. Although they are not preserved in

all specimens, among the most conspicuous features of

Jamoytius are W-shaped, serially repeated structures.

Their disposition indicates that they were coincident with

the body outline, or at least very nearly so (Pl. 1; Text-

fig. 4A). Each W extends around the majority of the lat-

eral body margin, leaving a gap on one body surface,

either dorsal or ventral (Pl. 1; Text-fig. 4D; Ritchie 1968,

pl. 4, fig. 1). The series of Ws does not extend along the

entire antero-posterior axis of the body; they are absent

from the anterior (e.g. Pl. 1) and their posterior limit is

uncertain. The Ws consist of alternating narrow and

broad zones.

The narrow zones are prominent and generally show

relief. They normally have a central area (200–300 lm

wide), the same colour as the matrix of the siltstone in

which the fossils are preserved, with very dark borders (c.

50 lm wide) on either side (Text-fig. 4C). In some

instances, the narrow zones also exhibit a tuberculate tex-

ture (Text-fig. 4E; Ritchie 1968, pl.4, fig. 3), which is best

observed on fragmentary specimens.

The broad zones (1–3 mm wide) lack relief, but are

darker in colour than other parts of the body. Within the

broad zones are linear features, lighter in colour; some of

these lines form dendritic patterns (Text-fig. 4C).

Elemental mapping of the W-shaped stripes of speci-

men GLAM V8141c shows that the borders of the narrow

zones and the whole of the broad zones contain associa-

tions of Ca and P (Text-fig. 2A) but not the other ele-

ments making up the matrix. Carbon is also present, but

appears to have an inverse distribution to that of Ca and

P; the W-shaped features are, therefore, interpreted as

being composed of calcium phosphate, possibly with an

organic component.

Axial lines and rounded structures. In the holotype (NHM

P11284a, Pl. 1, Text-fig. 5) and FR 1601 (Ritchie 1968; pl.

4, fig. 2, pl. 6, fig. 1), a pair of parallel, axial lines are

noted in the middle of the trunk (each approximately

2 mm width). Upon closer inspection, the lines are com-

posed of contiguous lozenge- or oval-shaped units, each

slightly longer than wide (Text-fig. 6B). In FR 1601, the

region between the axial lines preserves the W-shaped

structures from both the near and far side of the body,

whilst the region outside of the axial lines preserves the

Ws from only one side of the body (Text-fig. 6A). In

NHM P11284a, one of the axial lines bifurcates towards

the anterior. Towards the posterior of NHMP11284a, the

lines become less clear. Aligned with the axial lines are a

parallel and paired posterior series of dark, rounded

structures, which exhibit positive relief (Text-fig. 6B).

A C

PCa

CB

TEXT -F IG . 2 .9 SEM back scatter and elemental maps. A, W-

shaped structures of GLAM V8141c (back scatter; C, Carbon;

Ca, Calcium; P, Phosphorous). B, Anterior subcircle NHM

47787A (back scatter; C, Carbon).

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SANSOM ET AL . : TAPHONOMY AND AFFINITY OF AN ENIGMATIC SILURIAN VERTEBRATE 15

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Their periodicity is approximately the same as that of the

W-shaped structures. The alignment of the axial rounded

structures with the axial lines, combined with the loz-

enge-shaped units of the lines, suggests that the rounded

structures and axial lines may comprise the same struc-

ture.

Paired longitudinal ‘folds’. A pair of parallel linear features

resembling collapsed folds is observed on the same sur-

face of the body as the gap between the W-shaped struc-

tures (Pl. 1, Text-fig. 3). They originate posterior to the

serial subrectangles and continue posteriorly until they

become indistinct. They are generally straight and exhibit

wrinkling in some instances.

Reconstruction

The general two-dimensional form of fossils of Jamoytius

is presumed to be a result of the collapse of a soft body

A

C

D

B A

B

TEXT -F IG . 3 . 10Anterior subrectangles

with corresponding graphic

interpretations (A, B) and ventro-lateral

‘folds’ (C, D). A, NMS 1966.3.2. B, NMS

1965.59a. C, NMS 1966.3.2. D, NHM

P11285. Scale bars represent 5 mm.

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during decay rather than compaction, and body fossils in

different orientations can thus be equated to two-dimen-

sional views of a three-dimensional organism (Briggs and

Williams 1981). Most of the preserved features are evi-

dent in almost all the dorso-ventrally and laterally col-

lapsed specimens that retain the appropriate portion of

the body, and the three-dimensional architecture and

position of these features can therefore be confidently

modelled. Whilst the model is a simplification of some

features (e.g. anterior subcircles), it corresponds well with

all known specimens of Jamoytius, including those that

are obliquely collapsed (Text-fig. 7). The accuracy of the

model can be tested by its ability to predict the position

of features in any newly discovered specimens.

The antero-posterior axis and dorso-ventral and axis

are identified on the basis of the anatomical differentia-

tion in the ‘head’ and symmetrical disposition of surface

structures (e.g. paired subcircles and W-shaped struc-

tures), respectively; distinguishing dorsal and ventral

remains problematic in the absence of a phylogenetic

context. The model indicates that the paired axial lines

and allied rounded structures are likely to be interior

structures. They are preserved in only two specimens

(NHMP11284, oblique; FR1601, lateral) but it seems that

both lines occur in the sagittal plane. Towards the ante-

rior, one of the axial lines is very close to the surface with

no gap in Ws towards the anterior; towards the posterior,

the axial lines approach the midline.

ANATOMICAL INTERPRETATION ANDCHARACTER HOMOLOGY

Establishing a phylogenetic context

Historically, Jamoytius has been interpreted as a jawless

vertebrate, but it lacks any unequivocal vertebrate synapo-

morphies (e.g. sensory canals, brain, skull, muscular phar-

ynx, multi-chambered heart, liver, kidney etc.) or, for

that matter, any unequivocal chordate synapomorphies

(e.g. dorsal nerve chord, notochord, myomeres, endo-

style ⁄ thyroid, pharyngeal arches, postanal tail). Paired

sense organs can be reasonably interpreted as present in

Jamoytius, but these are not unique to chordates

(although within chordates, they are a vertebrate synapo-

morphy). Previous interpretations of Jamoytius as a verte-

brate or even chordate have, therefore, not been

adequately justified: anterior anatomical differentiation,

serial stripes, axial lines, and a fusiform and curved body

shape are not sufficient in themselves to support a chor-

date model. Such general conditions could be noted in a

broad range of metazoan taxa, for example, articulated

A

C D E

B

TEXT -F IG . 4 . W-shaped serially repeating stripes on the trunk of Jamoytius. A, NHM P11284a illustrating coincidence of stripes

with the left body margin. B, GLAM 101283 ⁄ 1. C, GLAM V8141. D, NHM P47784a. E, NHM P11284a. Scale bars represent 5 mm

(A–D) or 1 mm (E).

SANSOM ET AL . : TAPHONOMY AND AFFINITY OF AN ENIGMATIC SILURIAN VERTEBRATE 17

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soft-bodied fossils such as the purported polychaete Piec-

konia (e.g. Fitzhugh et al. 1997, fig. 7A.18). We can, how-

ever, compare Jamoytius with fossil or extant taxa that

possess the particular topological features outlined above.

Following redescription of Euphanerops (Janvier and

Arsenault 2007), it is clear that it shares with Jamoytius

the following features: dark anterior subcircles (specifi-

cally, a lateral pair, one terminal ring and one subtermi-

nal ring) and ladder-like rows of contiguous serially

repeating anterior subrectangles (Text-fig. 8). Two other

structures are comparable between the two genera but are

not present in exactly the same condition: serially repeat-

ing antero-posterior stripes and paired ventro-lateral

‘folds’. Unlike Jamoytius, Euphanerops also preserves some

unequivocal chordate synapomorphies (postanal tail,

terminal subcircle

subterminal subcirclelateral subcircle (l)

serial sub-

rectangles (l)

serial sub-

rectangles (r)

lateral subcircle (r)

ventro-lateral

folds

W-shaped

structures

axial line

(l/d)

axial line

(r/v)

linear rounded

structures

TEXT -F IG . 5 . Body parts and topological interpretation of the

holotype (NHM P11284a) of Jamoytius. Scale bar represents

10 mm.

ventralaxialline

dorsalaxialline

Ws on right(proximal)surface

Ws on left(distal) surface

dorsalaxialline

ventralaxialline

anteriorbifurcation

axial roundedstructures

Ws on dorso-lateralsurface

A A

B B

TEXT -F IG . 6 . Axial structures of Jamoytius. A, Trunk of FR

1601 with reconstruction illustrating paired axial lines. B, Trunk

of NHM P12284a with reconstruction illustrating paired axial

lines and axial rounded structures. A1 from Ritchie (1968, pl. 6,

fig. 1). Scale bars represent 5 mm.

8 PALAEONTOLOGY

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notochord) and vertebrate synapomorphies (mineralized

endoskeleton, anal fin with fin supports) (Janvier and

Arsenault 2007). Given the similarities between Jamoytius

and Euphanerops in body parts and their topological

relations, it is reasonable to infer that Jamoytius also

possessed a postanal tail and notochord, which are not

A B

C

TEXT -F IG . 7 . Different perspectives of the three-dimensional model compared with two-dimensional fossil specimens of Jamoytius

preserved in different orientations. A, Dorsal perspective with NHM P11284a. B, Ventral perspective with NMS 1966.3.2. C, Lateral

perspective (anterior-posterior axis slightly oblique) with NHM P11285. Scale bar represents 5 mm.

A

B

C

contiguous

subrectangles

median sub-

terminal subcircle

lateral

subcircles

TEXT -F IG . 8 . Anatomy of

Euphanerops and Jamoytius. A, MHNM

01-02 drawing illustrating some of the

features shared with Jamoytius. B,

Reconstruction of Euphanerops. C.

Reconstruction of Jamoytius in light of

new data. A from Janvier and Arsenault

(2007, fig. 3B2), B from Janvier and

Arsenault (2002, fig. 1b).Scale bar

represents 10 mm (A).

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preserved in known specimens. We reject the alternative

hypothesis that the similarities between Jamoytius and

Euphanerops are mere coincidences, on grounds of parsi-

mony. A chordate context for the interpretation of the

body parts of Jamoytius is thus justified, and topology can

be translated into anatomy in the light of this compara-

tive model (Table 1).

Anterior subcircles and subrectangles

Anatomical interpretation. Given a chordate model, the

lateral paired anterior subcircles are best interpreted as

optic capsules. The positions of the optic capsules of

Jamoytius can be interpreted as dorso-lateral given that in

all chordates with eyes they are located on either lateral

or dorso-lateral surfaces (rare exceptions include the ven-

tro-lateral eyes of the bighead carp, Hypophthalmichthys

nobilis). The dorsal and ventral surfaces of Jamoytius are

thereby identified – the optic capsules are dorsal, and the

gap between the W-shaped structures is along the ventral

surface.

Of the median anterior subcircles, the large rounded

subterminal ring, which is now clarified as being located

on the ventral body surface, is best interpreted as the oral

opening. Its position and architecture are consistent with

its interpretation as an annular cartilage (e.g. Ritchie

1963, 1968), such as that found in the extant lampreys.

There are, however, no associated structures preserved

that might support that hypothesis (e.g. circum oral teeth,

copular cartilages, oral papillae). The smaller, terminal

subcircle is comparable to the single nasal opening

observed in a number of jawless vertebrates, both extant

and extinct. Its terminal position indicates that it is unli-

kely to be a pineal organ.

The paired, serially repeating subrectangles compare

closely to the branchial openings observed in fossil jawless

vertebrates such as Euphanerops, osteostracans, and, to a

lesser extent, extant jawless vertebrates such as lampreys.

These animals possess a series of external branchial

openings, which originate in the head region and descend

ventrally towards the posterior. In Jamoytius, the subrec-

tangles have previously been interpreted as internal, akin

to the branchial basket of lampreys (Ritchie 1963, 1968;

Forey and Gardiner 1981; Janvier 1981) and as such

would be lateral to the gills. The coincidence of the struc-

tures with the body margin makes them more comparable

with cartilaginous trematic rings surrounding the external

branchial openings. The Jamoytius subrectangles are, how-

ever, contiguous and numerous, unlike the trematic rings

of lampreys.

The apparent variability in the number of paired bran-

chial openings (10 or more pairs) may be because of the

nature of preservation of these features but could also

reflect real differences in the number of branchial struc-

tures; intraspecific variation in the number of branchial

units occurs in some jawless vertebrates (i.e. hagfishes).

Taphonomy and composition. Since Ritchie’s (1963)

description of Jamoytius, the features of the anterior have

generally been accepted as components of a cartilaginous

endoskeleton in part because of their inferred decay resis-

tance and similarity to that of lampreys. Jawless vertebrate

cartilages are quite varied in composition, both within

and between clades (e.g. Wright et al. 1998; Zhang et al.

2006), and this variability seemingly affects their decay

resistance (R. Sansom, pers. obs.). There are no definite

fossil precedents for the preservation of cartilage as

organic films (Euphanerops remains equivocal (Janvier

and Arsenault 2002, 2007), whilst interpretations for con-

odonts (e.g. Aldridge and Theron 1993) have been made

through comparison with Jamoytius). This does not in

itself rule out Ritchie’s (1963, 1968) interpretation of a

cartilaginous endoskeleton in Jamoytius, however. With-

out analytical determination of the biomolecular compo-

sition of these features (which may be impossible in these

fossils), their interpretation must rely solely on compara-

tive anatomy and comparative taphonomy.

The uniform preservation of the anterior structures as

dark, flat films, coupled with their carbonaceous compo-

sition, is consistent with organic preservation. Further-

more, their wrinkles and folds indicate flexibility at the

time of collapse; the absence of evidence of brittle defor-

mation indicates they were not rigid. Ductile deformation

need not rule out their interpretation as cartilaginous

supports for body openings (e.g. annular and trematic

rings), because cartilage, including that of jawless

vertebrates, can exist in both rigid and flexible forms,

but it does prompt consideration of other potential

body margin-related biomolecules. For example, high

concentrations of melanin are found in association with

TABLE 1 . Topological features identified in Jamoytius and

their anatomical interpretations based upon a chordate compar-

ator.

Topological feature Anatomical interpretation

Anterior subcircles

(paired, lateral)

Optic capsules

Anterior subcircle

(terminal)

Single, terminal, nasal

opening

Anterior subcircle

(subterminal)

Round ventral mouth

Anterior subrectangles Multiple external branchial

openings

W-shaped structures Rigid (probably mineralised)

scales

Axial lines with subunits Axial skeleton

Ventro-lateral paired ‘folds’ Lateral fin folds?

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photosensory structures of lampreys (e.g. optic capsules,

pineal organ, lateral line system (Young 1981)) and other

body openings (e.g. branchial (Bagenal 1973)). The distri-

bution of melanin in lampreys is, therefore, consistent

with the interpretation of the anterior structures of

Jamoytius having originally had a high melanin content.

Currently, we are unable to determine whether the

anterior structures of Jamoytius were melanin or cartilage.

Regardless of whether they represent cartilaginous sup-

ports for body openings or skin pigment surrounding the

body openings, the anterior subcircles and subrectangles

are still best interpreted as a mouth, nasal opening, eyes

and external branchial openings.

W-shaped structures

Anatomical interpretations. A number of fossil jawless ver-

tebrates exhibit serial V-, W- or Z-shaped bands along

the body. These have been interpreted either as myomeres

(e.g. Haikouichthys, conodonts) or external dermoskeletal

scales (osteostracans, certain anaspids). Similarly, the W-

shaped structures of Jamoytius have been interpreted as

muscle blocks (Forey and Gardiner 1981; White 1946)

and as scales, either mineralized (Ritchie 1960) or unmin-

eralized, ‘horny’ and carbonized (Ritchie 1968, 1984).

Others regard any interpretations of these structures as

equivocal (Janvier 1981).

The Ws of Jamoytius appear to be single units, rather

than a series of subunits arranged in a W-shape, as is the

case in the scales of most vertebrates. Euphanerops also

shows long, undivided structures that run the height of

its flank, yet it is uncertain whether they are scales or

myomeres (Janvier and Arsenault 2007).

Taphonomy and composition. The narrow zones of the W-

shaped structures have undergone brittle deformation in

the form of fracturing and displacement in several speci-

mens (Text-fig. 4D), thus indicating that they were rigid

prior to collapse or compaction. Interpretation of the Ws

as scales is supported by their rigid nature, tubercular

ornamentation, preservation in relief and coincidence

with the body margin.

The W-shaped structures are phosphatic and rigid,

demonstrating a very different taphonomic history to the

anterior features (carbonaceous composition and ductile

deformation). It is important to consider whether the

phosphate of the Ws is primary or secondary. Within the

Jamoytius horizon, primary phosphate occurs, for exam-

ple, in the dermal denticles of the thelodont Loganellia

(Marss and Ritchie 1998) and secondary phosphate is

known in the form of fibrous mineralized muscle in the

arthropod Ainiktozoon (Van Der Brugghen et al. 1997).

The texture and colour of the phosphate of Jamoytius

does not directly compare to either of these phosphates,

so its nature remains unclear. The fracturing of the scales

does, however, support the hypothesis that the scales were

biomineralized in vivo, prior to their deformation.

No evidence is found for the muscle fibres identified

by White (1946). It seems likely that this was a misinter-

pretation of the dendritic pattern of the broad zone

(Ritchie 1968), which cannot be reconciled with any fea-

ture of a myomere (Text-fig. 4C). The dendritic pattern

occurs on specimens that have not been treated with hy-

droflouric acid (contra Forey and Gardiner 1981), but not

on any specimen that exhibits tubercles. The variation in

the appearance of scales among specimens may, therefore,

relate to the level of the splitting of the scale passing

through different hard tissues. This is observed in some

osteostracans (R. Sansom, pers. obs.), in which the mid-

dle layer of the dermoskeleton can be exposed revealing a

dendritic pattern of ‘intra-areal’ canals (e.g. Denison

1947; Janvier 1996a; Sansom 2008). The relative thinness

of the scales of Jamoytius, however, is difficult to reconcile

with the hypothesis that the broad zone dendritic pattern

represents a canal system. Alternatively, the pattern could

be an artefact caused by taphonomic processes such as

fracture because of post-mortem shrinkage of the broad

zones.

Axial lines with subunits

Anatomical interpretation. The linear, dorsal and ventral

axial lines and their continuation posteriorly as lines of

rounded axial features should be assessed through com-

parison with antero-posterior axial structures known in

vertebrates, i.e. notochord, dorsal nerve cord, gut and

vertebral elements. The contiguous lozenge ⁄oval subunits

are not consistent with previous interpretations as a noto-

chord and a gut (White 1946), or margins of a gut

(Ritchie 1968). A further inconsistency is the anterior

bifurcation of one of the lines (dorsal) that, contra to

Ritchie (1968), is not part of the branchial basket (Text-

fig. 5).

The internal pattern of subunits within the lines is

more in keeping with interpretation as an axial skeleton.

The contiguous nature of the subunits towards the ante-

rior and increasing separation towards the posterior is

comparable to the condition of the arcualia in lampreys

(Marinelli and Strenger 1954). The rounded or lozenge

shape of the elements in Jamoytius does not, however,

match the irregularly shaped cartilaginous arcualia of

either lampreys (a single series dorsal to notochord) or

Euphanerops (dorsal and ventral series, Janvier and Ar-

senault 2007: fig. 16). Rather, they are more comparable

to the ‘haemal series’ of Euphanerops, more specifically,

the lozenge-shaped subunits of the posterior haemal ser-

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ies. Although the notochord of modern jawless vertebrates

(hagfish and lampreys) is wide, the gap between the dor-

sal and ventral axial lines of Jamoytius is proportionally

far larger, potentially making interpretation as dorsal and

ventral arcualia problematic. Furthermore, the anterior

bifurcation of the dorsal line in NHM P12284 is inconsis-

tent with interpretation as arcualia.

Whilst it is not possible to determine precise homology

of the dorsal and ventral axial lines because of their unu-

sual shape and position, it is likely that they are formed

by subunits of some form of axial skeleton, either arcualia

in a previously unobserved condition or a ‘haemal series’

comparable to that of Euphanerops (Janvier and Arsenault

2007).

Taphonomy and composition. If interpretation of the dor-

sal and ventral axial lines of Jamoytius as axial skeleton is

accepted, then comparison with extant jawless vertebrates

indicates the subunits were likely composed of cartilage.

The seemingly different nature of the preservation of the

axial lines from that of the anterior subcircles ⁄ subrectan-

gles does not mean that they cannot both be composed

of cartilage: lamprey branchial cartilages have a different

composition from arcualial and neurocranial cartilages

(Fernandes and Eyre 1999; Robson et al. 1997).

Notochords interpreted in fossil jawless vertebrates

such as Gilpichthys (Bardack and Richardson 1977) and

conodonts (Aldridge et al. 1993) have a banded appear-

ance, seemingly because of overprinting of the myomeres.

In Jamoytius, evidence of myomeres is not preserved.

Whilst the W-shaped scales have a periodicity similar to

that of the axial line subunits, there are instances of the

narrow zones overlying the subunits. The subunits of the

axial lines of Jamoytius are, therefore, unlikely to be a

taphonomic artefact because of scales or myomere over-

printing. In FR 1601, the region between the dorsal and

ventral axial lines is the only region of the body to pre-

serve the W-shaped scales from both lateral sides of the

body (Text-fig. 6A). A similar pattern is observed in late-

stage decay of larval lampreys (e.g. Sansom et al. 2010),

which, when viewed laterally, reveal myomeres from both

lateral sides of the body within the region occupied by

the wide notochord, but not the dorsal and ventral sec-

tions of the body (R. Sansom, pers. obs.).

Paired longitudinal ‘folds’

Anatomical interpretation. The paired parallel ‘folds’ on

the ventro-lateral body margins (Text-fig. 3) have been

the source of conflicting interpretations. Some authors

regard them as ‘lateral fin folds’ (Janvier 1981; Ritchie

1968; White 1946), whilst others find no evidence to sup-

port that view (Forey and Gardiner 1981; Westoll 1958).

Long, thin, paired appendages (lateral fin folds) do not

occur in any form in extant vertebrates (Bemis and

Grande 1999), so we have compared the structures in

Jamoytius to those known in fossil jawless vertebrates.

Pharyngolepis (an anaspid) and Euphanerops possess long,

thin, paired ‘appendages’, which extend along the ventro-

lateral surfaces from the head to the anal region (Janvier

and Arsenault 2007; Ritchie 1964). In both of these taxa,

there are mineralized components of the ventro-lateral

appendages. Jamoytius lacks such mineralized structures,

and the ventro-lateral ‘folds’ are probably simple folds of

the skin.

Taphonomy and composition. Interpretation of the dorso-

ventral ‘folds’ as folds of skin without any form of

mineralized supports raises the question whether the

paired features are true anatomical features or a tapho-

nomic artefact. If the majority of the body surface was

covered with rigid scales (W-shaped structures), the more

flexible ventral surface in the gap between scales would be

prone to deformation during collapse. This hypothetical

taphonomic scenario is perhaps supported by the wrin-

kling that occurs within in the ventro-lateral folds of

some specimens but their paired nature argues against it

(Text-fig. 3). It is therefore unclear whether these folds

are distinct anatomical structures or merely a conse-

quence of body collapse; homologizing them with the

‘appendages’ of Pharyngolepis and Euphanerops is thus

currently problematic.

PHYLOGENETIC ANALYSIS

The evidence presented above indicates that Jamoytius is a

jawless vertebrate of uncertain affinities, so we have used

the most recent and comprehensive analysis of early ver-

tebrate interrelationships (Gess et al. 2006) as a basis to

investigate its precise phylogenetic position. The matrix of

Gess et al. (2006) is based upon earlier matrices (Janvier

1996b; Donoghue et al. 2000; Donoghue and Smith

2001), updated and expanded to include subsequently dis-

covered soft-bodied vertebrates, namely Haikouichthys

and Myllokunmingia (Shu et al. 1999; Donoghue et al.

2003; Hou et al. 2002), Mesomyzon (Chang et al. 2006)

and Priscomyzon (Gess et al. 2006) as well as oral charac-

ters relating to cyclostome monophyly.

Coding. The coding used for Jamoytius by Donoghue

et al. (2000) and subsequently by Donoghue and Smith

(2001) and Gess et al. (2006) was based upon an earlier

unpublished version of the data presented here (Freed-

man 1999), not all of which has survived subsequent

scrutiny. Thus, the coding has been modified to reflect

the interpretations herein (e.g. Table 1; Appendix S1).

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The matrix has also been updated to include additional

data for Euphanerops (Janvier and Arsenault 2007), Hai-

kouichthys (Zhang and Hou 2004), Arandaspida (Sansom

et al. 2005) and Galeaspida (Wang et al. 2005). Euphaner-

ops is taken to include Legendrelepis and Endiolepis (Jan-

vier 1996c; Janvier and Arsenault 2007). Two taxa from

the Middle Devonian of Scotland that have been pro-

posed to have affinities with Jamoytius have been added

to the matrix: Cornovichthys (Newman and Trewin 2001)

and Achanarella (Newman 2002).

Gess et al. (2006) employed presence ⁄ absence coding.

Such coding methodology violates the requirements of

logical independence of characters and can lead to false

support for a cladogram (Strong and Lipscomb 1999;

Forey and Kitching 2000). For example, absence of a nas-

ohypophyseal opening is counted twice in two different

characters (15 ⁄ 16), as is absence of dentine (80 ⁄ 81). The

matrix presented here therefore utilizes contingent coding,

which necessitates the erection of additional characters

(Appendix S1: characters 100–109). Furthermore, revision

of the coding and coding strategy for the characters relat-

ing to the relationships of extant cyclostomes reveals that

many of the physiological and miscellaneous characters

are uninformative (P. C. J. Donoghue, unpublished data).

These characters are removed here, whilst some of the

neurological characters are revised (e.g. cerebellar primor-

dia, retina).

Results. Heuristic searches, including all taxa, found two

most parsimonious trees of branch length 185 (Text-

fig. 9B). Jamoytius is placed as sister taxon to Euphaner-

ops, united by a ventral mouth and annular cartilage

(both homoplastic characters). These taxa (which could

together be termed Jamoytiiformes Tarlo, 1967) are

resolved as stem-gnathostomes because of their trunk der-

mal skeleton, separate anal fin and paired fin folds.

Ostraco/Jawed

Ostraco/Jawed

Tunicata

Cephalochordata

Myxinoidea

Myxinikela

Haikouichthys

Petromyzontida

Mesomyzon

Priscomyzon

Mayomyzon

Euconodonta

Jamoytius

Euphanerops

Anaspida

Loganellia

Turinia

Heterostraci

Arandaspida

Astraspis

Galeaspida

Osteostraci

Jawed Vertebrates

1

1

1

1

1

1

2

2

2

1

1

1

3

1

Achanarella

Cornovichthys

1

1

2

Myxinoidea

Petromyzontida

Anaspida

Jamoytius

Ostraco/Jawed

Myxinoidea

Petromyzontida

Anaspida

Jamoytius

Ostraco/Jawed

Euphanerops

Myxinoidea

Petromyzontida

Anaspida

Jamoytius

Ostraco/Jawed

Euphanerops

Euconodonta

Pteraspidimorphi

Myxinoidea

Petromyzontida

Anaspida

Jamoytius

Euphanerops

Euconodonta

Myxinoidea

Petromyzontida

Anaspida

Jamoytius

Euphanerops

Euconodonta

Pteraspidimorphi

Myxinoidea

Petromyzontida

Anaspida

Jamoytius

Ostraco/Jawed

Euphanerops

Euconodonta

Forey 1995 Janvier 1996b Donoghue et al. 2000 Donoghue et al. 2001 Shu et al. 2003 Gess et al. 2006A

B C Tunicata

Cephalochordata

Myxinoidea

Myxinikela

Haikouichthys

Petromyzontida

Mesomyzon

Priscomyzon

Mayomyzon

Euconodonta

Jamoytius

Euphanerops

Anaspida

Loganellia

Turinia

Heterostraci

Arandaspida

Astraspis

Galeaspida

Osteostraci

Jawed Vertebrates

1

1

1

1

1

1

1

1

2

1

1

1

2

1

Achanarella

Cornovichthys

1

1

2 1

1

TEXT -F IG . 9 . Phylogenetic relationships of Jamoytius. A, simplified versions of previous cladistic analyses of Forey (1995), Janvier

(1996b), Donoghue et al. (2000), Donoghue and Smith (2001), Shu et al. (2003), and Gess et al. (2006) where Ostraco ⁄ Jawed

represents other ostracoderms and jawed vertebrates. B, single most parsimonious tree from the unconstrained phylogenetic analysis

with decay support indices. C, Strict consensus of trees resulting from analysis constrained for cyclostome monophyly with decay

indices.

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Whether Jamoytius preserves these latter two characters is

uncertain, but the same topology results when the paired

appendages of Jamoytius are coded as unknown. Jamoytii-

formes are placed closer to the root of total-group gnat-

hostomes than Anaspida because of an absence of dermal

head covering, dentine and lamellar aspidin. Close rela-

tionships between Jamoytius and Euphanerops have been

reconstructed in previous phylogenetic studies (Janvier

1996a–c; Donoghue et al. 2000; Donoghue and Smith

2001; Shu et al. 2003), but always as part of a clade with

Anaspida (Text-fig. 9A).

Of the other taxa proposed to have jamoytiiform

affinities, Cornovichthys is placed as a stem-vertebrate

(in the sense that Petromyzontida and Gnathostomata

comprise Vertebrata, whilst vertebrates and Myxinoidea

constitute Craniata (Janvier (1981)), whilst Achanarella

is placed as a stem-gnathostome in a more basal posi-

tion than (Jamoytius + Euphanerops). Neither taxon is,

therefore, resolved as part of a monophyletic Jamoytii-

formes.

The revisions incorporated in the data matrix used here

also led to other changes in relationships among jawless

vertebrates. Changing the coding strategy for dentine and

odontodes has led to the thelodonts (represented here by

Loganellia and Turinia) being identified as closer to the

root of total-group gnathostomes than the pteraspidimor-

phi (represented here by Heterostraci, Arandaspida and

Astraspis) on the gnathostome stem lineage. Furthermore,

eucondonts are placed as sister taxon to fossil and extant

lampreys, making conodonts stem-petromyzontids. Lam-

preys and euconodonts are united by possession of trans-

versely biting teeth.

Morphological evidence, both neontological and palae-

ontological, consistently finds lampreys (Petromyzontida)

as more closely related to jawed vertebrates than hagfishes

(Myxinoidea), as is the case here (Løvtrup, 1977; Janvier,

1981; Forey, 1984; Khonsari et al. 2009). Molecular inves-

tigations, however, identify the lampreys as more closely

related to the hagfishes and thus support cyclostome

monophyly (e.g. Delarbre et al. 2002; Delsuc et al. 2006).

Phylogenetic analysis of our data matrix constrained for

cyclostome monophyly identifies a less parsimonious

solution (branch length 191) with a topology very similar

to that of the unconstrained analysis, differing only in

placement of the myxinoids and resolution amongst petr-

omyzontids (Text-fig. 9C). The Jamoytiiformes are still

recovered as stem-gnathostomes, whilst the euconodonts

are recovered as stem-cyclostomes.

EVOLUTIONARY IMPLICATIONS

Jamoytius is commonly considered to represent a primi-

tive member of a fossil or extant vertebrate clade, either a

primitive anaspid (e.g. Ritchie 1963) or an ancestral lam-

prey (e.g. Mallat 1984). Despite the fact that a number of

its characters are plesiomorphic for chordates or for ver-

tebrates, analysis here establishes sister taxon relationship

with Euphanerops. In our unconstrained analysis, Jamoyti-

iformes represent a new grade in the evolution of stem-

gnathostomes, after the evolution of a trunk dermal skele-

ton but before the evolution of lamellar aspidin and der-

mal head skeleton. Given the preservation of trunk

dermoskeleton of Jamoytius (W-shaped scales), it is rea-

sonable to assume that any head dermoskeleton would

also be preserved if it had existed. The coding for absence

of head dermoskeleton in Jamoytius, and subsequent

placement of Jamoytiiformes on the gnathostome stem,

therefore reflects phylogenetic absence rather than tapho-

nomic loss (see Donoghue and Purnell 2009 for a discus-

sion of alternative meanings of stem assignments). The

position of Cornovichthys as a stem-vertebrate is sup-

ported by only one character (anterior otic capsules), the

interpretation of which is equivocal in some taxa. The

stem placements of Cornovichthys and Achanarella are

likely to reflect taphonomic bias resulting from loss of

characters through post-mortem decay (Donoghue and

Purnell 2009; Sansom et al. 2010). To further resolve the

relationships of the Jamoytiiformes and putatively related

taxa, reinterpretation of the relevant fossils is required

using the same principles as applied here for Jamoytius.

The phylogenetic placement of conodonts as stem-lam-

preys or stem-cyclostomes is contrary to the hypotheses

from previous analyses in which conodonts are placed as

stem-gnathostomes (Donoghue et al. 2000; Donoghue

and Smith 2001). The new placement is not robust, but it

is the most parsimonious on the basis of the morphologi-

cal data analysed here. The instability of this result sug-

gests that addition of further soft-bodied taxa to

phylogenetic matrices of early vertebrates will potentially

affect hypotheses of euconodont affinity. Our phyloge-

netic analysis does not raise any doubts about the place-

ment of euconodonts within the vertebrates.

Other stem-gnathostome taxa such as Pteraspidomor-

phi, Galeaspida and Osteostraci are resolved to be closer

to the gnathostome crown than thelodonts. This proposal

differs from previous suggestions of thelodont sister

relationships with gnathostomes (Marss et al. 2007),

chondrichthyes (Turner 1991) or the group (Galeasp-

ida + Osteostraci + jawed vertebrates) (Donoghue and

Smith 2001). Given the limited number of thelodont taxa

included here, however, questions of thelodont affinity

remain open to further investigation.

Jamoytius has often been cited in defence of the lateral

fin fold theory (e.g. Jarvik 1980; Shubin et al. 1997), an

evolutionary developmental scenario in which the paired

appendages of jawed vertebrates derive from continuous

ventro-lateral fin folds of jawless vertebrates by the loss of

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the intermediate portion of the fin fold (Balfour 1876;

Thacher 1877; reviewed by Coates 1994; Bemis and

Grande 1999). The present study found no evidence for

any skeletal or muscular structures that would allow an

assessment of potential homologies with the paired fins of

jawed vertebrates. Furthermore, the antero-posterior skin

folds may represent taphonomic artefacts. Our results

indicate that the structures of anaspids, thelodonts and

potentially Jamoytius were acquired independently of

paired fins restricted to the pectoral region in Osteostraci

and Gnathostomata (Sansom 2009).

CONCLUSIONS

The study of the anatomy of problematic organisms can

be aided by the use of a methodology designed to sepa-

rate topological and morphological reconstruction from

anatomical interpretation and to gather as much informa-

tion as possible about the preserved features through

taphonomic analyses. The application to Jamoytius dem-

onstrates that it is a vertebrate, with preserved W-shaped

phosphatic scales, ten or more paired external branchial

openings, dorso-lateral optic capsules, a round ventral

mouth, a terminal nasal opening, and, potentially, dorsal

and ventral axial skeleton. Interpretations of paired fins

remain equivocal. Analyses of the phylogenetic affinity of

Jamoytius identify a sister taxon relationship with Eupha-

nerops. This clade, the Jamoytiiformes, is a primitive

group of stem-gnathostomes and does not form a clade

with the Anaspida.

Acknowledgements. This work was funded in part by a Natural

Environment Research Council grant (NE ⁄ E015336 ⁄ 1 to SEG

and MAP). KF was supported by an Overseas Research Student

award (ORS ⁄ 96014039) and by R. A. Freedman. Various people

are thanked for their assistance in enabling the study and loan of

material including Sir Frederick Stewart, Peder Aspen (University

of Edinburgh), Neil Clark (Hunterian Museum), Bobbie Paton,

Liz Hide and Mike Taylor (National Museum of Scotland), Sally

Young, Peter Forey and Martha Ritcher (Natural History

Museum, London), Robert Jones and Alex Ritchie (Australian

Museum) and Steve Tunnicliff (British Geological Survey). Tony

Milodowski and Paul Wetton (British Geological Survey) kindly

assisted with SEM analysis. We also appreciate the constructive

comments of three anonymous reviewers and Philip Donoghue,

which have allowed us to improve the manuscript.

Editor. Philip Donoghue

SUPPORTING INFORMATION

Additional Supporting Information may be found in the online

version of this article:

Data S1. Xxxxxxxx. 3

Appendix S1. Character list and matrix used in phylogenetic

analysis – an updated version of Gess et al. (2006) with neuro-

logical characters adapted according to P. Donoghue (unpub-

lished data).

Please note: Wiley-Blackwell are not responsible for the con-

tent or functionality of any supporting materials supplied by the

authors. Any queries (other than missing material) should be

directed to the corresponding author for the article.

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